1. Field
The present disclosure relates to an insulation monitoring device that monitors the insulation state of a power system or a load apparatus connected to the power system (hereafter, this will also be referred to collectively as a power system).
2. Description of Related Art
So-called Igr type and IOr type are known as insulation monitoring methods for monitoring the insulation state of a power system, as described in Japanese Patent No. 4,738,274 (e.g., paragraphs [0005] to [0011], FIG. 13, and FIG. 14).
Of these, the Igr type is such that a supervisory signal of a predetermined frequency differing from the system frequency is implanted in the grounding wire of a power receiving transformer, the supervisory signal, which has flowed back via a ground electrical capacitor or ground insulation resistor, is extracted from the system wiring, and the insulation state of the power system is monitored by the size of a resistance component current included in the extracted supervisory signal being compared with a predetermined monitoring setting value.
Also, the I0r type is such that, rather than a supervisory signal being implanted in the power system, a resistance component current of the same phase as the voltage to ground of the system is extracted from a zero-phase current flowing through the grounding wire of a power receiving transformer, and the insulation state of the power system is monitored by the size of the resistance component current being compared with a predetermined monitoring setting value.
Meanwhile, it is known that when the load apparatus is a large capacity inverter or the like, a noise filter including at least a capacitor is connected to the input side of the load apparatus.
FIG. 13 shows the whole configuration of an Igr type insulation monitoring device applied to a power system including this kind of load apparatus and noise filter.
In FIG. 13, 10 is a power receiving transformer, 11 is a grounding wire connected to the secondary side thereof, 20 is wiring, 21 is a circuit breaker provided in the wiring 20, 22 is a ground electrical capacitor, 23 is a ground insulation resistor, 30 is a load apparatus such as a large capacity inverter, 31 is a noise filter (capacitive filter) having a capacitor, 41 is a supervisory signal superimposing unit for superimposing a supervisory signal on the grounding wire, 42 is a monitoring device main body that carries out insulation monitoring by extracting a resistance component current of the same phase as a reference voltage, to be described hereafter, from leakage current flowing through the grounding wire 11, carries out alarm output, and the like, and 43 is a reference voltage measurement unit that measures the voltage of the grounding wire 11 as the reference voltage.
Next, FIG. 14 is a block diagram showing the basic configuration of the monitoring device main body 42.
The monitoring device main body 42 is such that a frequency component the same as the supervisory signal is extracted from a reference voltage Vst and leakage current IO by frequency extraction units 42a and 42b, and a resistance component current Igr of the same phase as the reference voltage Vst is extracted by an Igr extraction unit 42c. Further, an insulation evaluation unit 42d compares the size of the resistance component current Igr with a predetermined monitoring setting value Irref, determines that there is an insulation failure when Igr exceeds the monitoring setting value Irref, and sends a signal to an alarm output unit 42e, thus causing an appropriate alarm to be output by a visual display or signal transmission to the exterior.